Do some practice tests from websites or from a book on Scholastic aptitude tests for the last few years. If you could do many of them with confidence , then you can do well in exams.
Familiarize your self with the pattern of the questions, sections etc. See the difficulty of questions. Usually the first 50% of the questions are simple enough. Last few questions could be difficult. So answer as many as you can from the beginning.
Keep cool. Think of smart ways and simple ways. Laborious ways perhaps not right.
At times, you can eliminate the bad options quickly, rather than finding the correct answer.
You can carry calculator perhaps. Find out.
You need a few good practice sessions to give you the speed. Some questions could be a little tricky. Though easy, you may overlook. So do not rush, but do fast.
There are negative marks for wrong answers. so it is preferable to write correct ones. If in doubt, perhaps leave it alone.
If we know which subjects you are writing, then we can put forward more tips.